GeezerVison

The World Wide Web, restored to 800 pixels of glory.

GeezerVison is showing github.com — gh-159111: Update vendored mimalloc to v2.5.2 by corona10 · Pull Request #159112 · python/cpython

Conversation

corona10 commented Oct 10, 2026 •

edited by bedevere-app Bot

Loading

Uh oh!

There was an error while loading. Please reload this page.

Copy link

Copy Markdown

Member

Issue: Upgrade mimalloc version from 2.1.2 to 2.5.2 #159111

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

All reactions

bedevere-app Bot added the type-feature A feature request or enhancement label

Oct 10, 2026

bedevere-app Bot mentioned this pull request

Oct 10, 2026

Upgrade mimalloc version from 2.1.2 to 2.5.2 #159111

Closed

corona10 self-assigned this

Oct 10, 2026

corona10 added the 🔨 test-with-refleak-buildbots Test PR w/ refleak buildbots; report in status section label

Oct 10, 2026

bedevere-bot commented Oct 10, 2026

Copy link

Copy Markdown

🤖 New build scheduled with the buildbot fleet by @corona10 for commit 2649e2b 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F159112%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-refleak-buildbots label again.

All reactions

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

bedevere-bot removed the 🔨 test-with-refleak-buildbots Test PR w/ refleak buildbots; report in status section label

Oct 10, 2026

corona10 marked this pull request as ready for review

October 10, 2026 11:25

corona10 requested review from a team, AA-Turner, FFY00, ZeroIntensity, emmatyping, ericsnowcurrently, erlend-aasland and itamaro as code owners

October 10, 2026 11:25

bedevere-app Bot added the awaiting core review label

Oct 10, 2026

corona10 requested a review from mpage

October 10, 2026 11:25


          Update vendored mimalloc to v2.5.2

4180f6d

Upgrade mimalloc from v2.1.2 to v2.5.2 as-is from upstream.

v2.1.2: https://github.com/microsoft/mimalloc/releases/tag/v2.1.2
v2.5.2: https://github.com/microsoft/mimalloc/releases/tag/v2.5.2

corona10 force-pushed the gh-159111 branch from 2649e2b to f81e6c2 Compare

October 10, 2026 11:29

corona10 added the 🔨 test-with-refleak-buildbots Test PR w/ refleak buildbots; report in status section label

Oct 10, 2026

bedevere-bot commented Oct 10, 2026

Copy link

Copy Markdown

🤖 New build scheduled with the buildbot fleet by @corona10 for commit f81e6c2 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F159112%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-refleak-buildbots label again.

All reactions

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

bedevere-bot removed the 🔨 test-with-refleak-buildbots Test PR w/ refleak buildbots; report in status section label

Oct 10, 2026

corona10 commented Oct 10, 2026

Copy link

Copy Markdown

Member Author

@mpage, could you trigger a free-threading benchmark for this change? :)

mpage reacted with thumbs up emoji

All reactions

👍 1 reaction

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

read-the-docs-community Bot commented Oct 10, 2026 •

edited

Loading

Uh oh!

There was an error while loading. Please reload this page.

Copy link

Copy Markdown

Documentation build overview

📚 cpython-previews | 🛠️ Build #35145094 | 📁 Comparing 09196b1 against main (88fd5fe)

🔍 Preview build

85 files changed · ± 85 modified

± Modified

All reactions

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

corona10 added the 🔨 test-with-refleak-buildbots Test PR w/ refleak buildbots; report in status section label

Oct 10, 2026

bedevere-bot commented Oct 10, 2026

Copy link

Copy Markdown

🤖 New build scheduled with the buildbot fleet by @corona10 for commit 222601b 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F159112%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-refleak-buildbots label again.

All reactions

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

bedevere-bot removed the 🔨 test-with-refleak-buildbots Test PR w/ refleak buildbots; report in status section label

Oct 10, 2026

corona10 commented Oct 10, 2026

Copy link

Copy Markdown

Member Author

I will fix MSAN later:

==11983==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x55e368c48377 in _mi_random_next /home/runner/work/cpython/cpython/Objects/mimalloc/random.c:158:3
    #1 0x55e368c48377 in _mi_heap_random_next /home/runner/work/cpython/cpython/Objects/mimalloc/heap.c:281:10
    #2 0x55e368c48377 in mi_heap_main_init /home/runner/work/cpython/cpython/Objects/mimalloc/init.c:220:29
    #3 0x55e368c49eaf in _mi_auto_process_init /home/runner/work/cpython/cpython/Objects/mimalloc/init.c:568:3
    #4 0x7f8aa762aa53 in __libc_start_main (/usr/lib/x86_64-linux-gnu/libc.so.6+0x2aa53) (BuildId: 4ec69afdf3da96ce7388640dcd27c6d0c1b256ef)
    #5 0x55e36886ee24 in _start (/home/runner/work/cpython/cpython/Programs/_freeze_module+0xb4e24) (BuildId: 5e5dc085937d530e3b49b31b09d53deb8664a51d)

  Uninitialized value was stored to memory at
    #0 0x55e368c8b8a0 in chacha_block /home/runner/work/cpython/cpython/Objects/mimalloc/random.c:67:20
    #1 0x55e368c47beb in chacha_next32 /home/runner/work/cpython/cpython/Objects/mimalloc/random.c:83:5
    #2 0x55e368c47beb in _mi_random_next /home/runner/work/cpython/cpython/Objects/mimalloc/random.c:154:22
    #3 0x55e368c47beb in _mi_heap_random_next /home/runner/work/cpython/cpython/Objects/mimalloc/heap.c:281:10
    #4 0x55e368c47beb in mi_heap_main_init /home/runner/work/cpython/cpython/Objects/mimalloc/init.c:220:29
    #5 0x55e368c49eaf in _mi_auto_process_init /home/runner/work/cpython/cpython/Objects/mimalloc/init.c:568:3
    #6 0x7f8aa762aa53 in __libc_start_main (/usr/lib/x86_64-linux-gnu/libc.so.6+0x2aa53) (BuildId: 4ec69afdf3da96ce7388640dcd27c6d0c1b256ef)
    #7 0x55e36886ee24 in _start (/home/runner/work/cpython/cpython/Programs/_freeze_module+0xb4e24) (BuildId: 5e5dc085937d530e3b49b31b09d53deb8664a51d)

  Uninitialized value was stored to memory at
    #0 0x55e368c5d150 in chacha_init /home/runner/work/cpython/cpython/Objects/mimalloc/random.c:109:23
    #1 0x55e368c5d150 in mi_random_init_ex /home/runner/work/cpython/cpython/Objects/mimalloc/random.c:201:3
    #2 0x55e368c47b57 in _mi_random_init /home/runner/work/cpython/cpython/Objects/mimalloc/random.c:205:3
    #3 0x55e368c47b57 in mi_heap_main_init /home/runner/work/cpython/cpython/Objects/mimalloc/init.c:218:7
    #4 0x55e368c49eaf in _mi_auto_process_init /home/runner/work/cpython/cpython/Objects/mimalloc/init.c:568:3
    #5 0x7f8aa762aa53 in __libc_start_main (/usr/lib/x86_64-linux-gnu/libc.so.6+0x2aa53) (BuildId: 4ec69afdf3da96ce7388640dcd27c6d0c1b256ef)
    #6 0x55e36886ee24 in _start (/home/runner/work/cpython/cpython/Programs/_freeze_module+0xb4e24) (BuildId: 5e5dc085937d530e3b49b31b09d53deb8664a51d)

  Uninitialized value was created by an allocation of 'key' in the stack frame
    #0 0x55e368c5cbad in mi_random_init_ex /home/runner/work/cpython/cpython/Objects/mimalloc/random.c:181:3

SUMMARY: MemorySanitizer: use-of-uninitialized-value /home/runner/work/cpython/cpython/Objects/mimalloc/random.c:158:3 in _mi_random_next
Exiting

All reactions

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.


          Re-apply CPython-specific changes to mimalloc v2.5.2

836dced

Most of the previous downstream changes were upstreamed in mimalloc
v2.1.3 - v2.1.7 (heap tags, _mi_heap_init/_mi_tld_init, MI_PRIM_THREAD_ID,
sub-processes, heap walk optimizations, platform fixes) and are dropped.

Remaining CPython-specific changes, all marked with a "CPython" comment:

- QSBR delayed page freeing for free-threaded builds (pythongh-115103,
  pythongh-145615): mi_page_t/mi_heap_t fields and _PyMem_mi_* hooks in
  page.c, heap.c and segment.c.
- debug_offset: preserve the first bytes of a PyObject (ob_tid, refcount
  fields) when filling freed or uninitialized memory in debug builds
  (pythongh-115491).
- Atomic mi_block_t.next loads/stores to avoid TSAN reports (pythongh-129748).
- Relax the owning thread assertion in _mi_free_delayed_block for
  free-threaded builds, since the GC traverses heaps of other threads.
- Call _mi_heap_delayed_free_partial() in mi_heap_visit_blocks()
  (pythongh-112532).
- Only count reclaimed pages up to MI_MEDIUM_OBJ_SIZE_MAX as a
  "right page" in mi_segment_reclaim (pythongh-115103).
- Rename the weak _ZSt15get_new_handlerv symbol and disable the
  mi_is_in_heap_region debug warning.
- Zero-initialize _mi_page_empty instead of a positional initializer.

corona10 force-pushed the gh-159111 branch from ceb117e to 5fb37d1 Compare

October 10, 2026 13:42

bedevere-bot commented Oct 13, 2026

Copy link

Copy Markdown

🤖 New build scheduled with the buildbot fleet by @corona10 for commit 8b9cb49 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F159112%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-refleak-buildbots label again.

All reactions

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

bedevere-bot removed the 🔨 test-with-refleak-buildbots Test PR w/ refleak buildbots; report in status section label

Oct 13, 2026

mpage commented Oct 13, 2026

Copy link

Copy Markdown

Contributor

@corona10 - Kicked off another run. Fingers crossed this one works.

corona10 reacted with thumbs up emoji

All reactions

👍 1 reaction

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

mpage commented Oct 13, 2026

Copy link

Copy Markdown

Contributor

@corona10 - New results

All reactions

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

corona10 commented Oct 13, 2026

Copy link

Copy Markdown

Member Author

@mpage

Okay benchmark result now looks good to me since there is no significant change

fork: corona10
ref: gh_159111
machine: linux-x86_64
commit hash: 8b9cb49
commit date: 2026-10-13
overall geometric mean: 1.003x faster
HPT reliability: 97.78%
HPT 99th percentile: 1.00x faster
Memory change: 1.00x

Would you like to review this PR?

All reactions

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.


          Merge remote-tracking branch 'upstream/main' into pythongh-159111

09196b1

corona10 assigned DinoV

Oct 20, 2026

corona10 mentioned this pull request

Oct 20, 2026

gh-131999: Add support for tvOS, visionOS and watchOS. #159944

Merged

corona10 commented

Oct 22, 2026

View reviewed changes

Comment thread

Doc/whatsnew/3.16.rst

Comment on lines +1171 to +1175

		* Update the bundled `mimalloc library`_ from version 2.1.2 to 2.5.2.
		(Contributed by Donghee Na in :gh:`159111`.)

		.. _mimalloc library: https://github.com/microsoft/mimalloc/

corona10 Oct 22, 2026

Copy link

Copy Markdown

Member Author

There was a problem hiding this comment.

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Suggested change

	* Update the bundled `mimalloc library`_ from version 2.1.2 to 2.5.2.
	(Contributed by Donghee Na in :gh:`159111`.)

	.. _mimalloc library: https://github.com/microsoft/mimalloc/

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

All reactions

corona10 Oct 22, 2026

Copy link

Copy Markdown

Member Author

There was a problem hiding this comment.

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Because for the main branch, we will target v3.

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

All reactions

corona10 commented Oct 22, 2026

Copy link

Copy Markdown

Member Author

cc @DinoV

All reactions

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

DinoV approved these changes

Oct 22, 2026

View reviewed changes

DinoV left a comment

Copy link

Copy Markdown

Contributor

There was a problem hiding this comment.

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This looks good!

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

All reactions

bedevere-app Bot added awaiting merge and removed awaiting core review labels

Oct 22, 2026

corona10 added needs backport to 3.14

bugs and security fixes

needs backport to 3.15 bugs and security fixes labels

Oct 22, 2026

corona10 merged commit aff7a2e into python:main

Oct 22, 2026

63 of 64 checks passed

Uh oh!

There was an error while loading. Please reload this page.

miss-islington-app Bot commented Oct 22, 2026

Copy link

Copy Markdown

Thanks @corona10 for the PR 🌮🎉.. I'm working now to backport this PR to: 3.14, 3.15.
🐍🍒⛏🤖

All reactions

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

bedevere-app Bot removed the awaiting merge label

Oct 22, 2026

miss-islington-app Bot commented Oct 22, 2026

Copy link

Copy Markdown

Sorry, @corona10, I could not cleanly backport this to 3.15 due to a conflict.

Please backport manually with cherry_picker, see the devguide for more information.

cherry_picker aff7a2e23bd6ed68fa15c1ceda94a2fdd7f8cf7f 3.15

All reactions

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

miss-islington-app Bot unassigned DinoV

Oct 22, 2026

miss-islington-app Bot commented Oct 22, 2026

Copy link

Copy Markdown

Sorry, @corona10, I could not cleanly backport this to 3.14 due to a conflict.

Please backport manually with cherry_picker, see the devguide for more information.

cherry_picker aff7a2e23bd6ed68fa15c1ceda94a2fdd7f8cf7f 3.14

All reactions

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

corona10 added the sprint label

Oct 22, 2026

corona10 added a commit to corona10/cpython that referenced this pull request

Oct 22, 2026


          [3.15] pythongh-159111: Update vendored mimalloc to v2.5.2 (pythongh-…

265f0fb

…159112)

* Update vendored mimalloc to v2.5.2

Upgrade mimalloc from v2.1.2 to v2.5.2 as-is from upstream.

v2.1.2: https://github.com/microsoft/mimalloc/releases/tag/v2.1.2
v2.5.2: https://github.com/microsoft/mimalloc/releases/tag/v2.5.2

* Re-apply CPython-specific changes to mimalloc v2.5.2

Most of the previous downstream changes were upstreamed in mimalloc
v2.1.3 - v2.1.7 (heap tags, _mi_heap_init/_mi_tld_init, MI_PRIM_THREAD_ID,
sub-processes, heap walk optimizations, platform fixes) and are dropped.

Remaining CPython-specific changes, all marked with a "CPython" comment:

- QSBR delayed page freeing for free-threaded builds (pythongh-115103,
  pythongh-145615): mi_page_t/mi_heap_t fields and _PyMem_mi_* hooks in
  page.c, heap.c and segment.c.
- debug_offset: preserve the first bytes of a PyObject (ob_tid, refcount
  fields) when filling freed or uninitialized memory in debug builds
  (pythongh-115491).
- Atomic mi_block_t.next loads/stores to avoid TSAN reports (pythongh-129748).
- Relax the owning thread assertion in _mi_free_delayed_block for
  free-threaded builds, since the GC traverses heaps of other threads.
- Call _mi_heap_delayed_free_partial() in mi_heap_visit_blocks()
  (pythongh-112532).
- Only count reclaimed pages up to MI_MEDIUM_OBJ_SIZE_MAX as a
  "right page" in mi_segment_reclaim (pythongh-115103).
- Rename the weak _ZSt15get_new_handlerv symbol and disable the
  mi_is_in_heap_region debug warning.
- Zero-initialize _mi_page_empty instead of a positional initializer.

* Update the free-threaded build to mimalloc v2.5.2 changes

mimalloc v2.1.4 replaced the list of abandoned segments with per-arena
bitmaps and introduced sub-processes (mi_subproc_t) to keep abandoned
segments of separate interpreters apart. Use them instead of the
CPython-specific mi_abandoned_pool_t:

- Each interpreter owns a mi_subproc_t created in init_interpreter().
- tstate_mimalloc_bind() sets tld->segments.subproc and uses the
  upstream _mi_heap_init() signature.
- The GC and sys.getallocatedblocks() visit abandoned segments with
  _PyMem_mi_visit_abandoned_blocks(), the upstream cursor API without
  the mi_option_visit_abandoned requirement, while STW.

* Update NEWS.d

* fix MSAN

* fix TSAN

* fix test_cext

* Disable THP

* Address code review

* Address code review

* Address code review

* nit

* Address code review

* Address code review
(cherry picked from commit aff7a2e)

Co-authored-by: Donghee Na <[email protected]>

bedevere-app Bot commented Oct 22, 2026

Copy link

Copy Markdown

GH-160178 is a backport of this pull request to the 3.15 branch.

All reactions

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

bedevere-app Bot removed the needs backport to 3.15 bugs and security fixes label

Oct 22, 2026

bedevere-app Bot commented Oct 22, 2026

Copy link

Copy Markdown

GH-160183 is a backport of this pull request to the 3.14 branch.

All reactions

Sorry, something went wrong.

Uh oh!

There was an error while loading. Please reload this page.

bedevere-app Bot removed the needs backport to 3.14 bugs and security fixes label

Oct 22, 2026

corona10 deleted the gh-159111 branch

October 22, 2026 07:52

corona10 added a commit that referenced this pull request

Oct 22, 2026


          [3.14] gh-159111: Update vendored mimalloc to v2.5.2 (gh-159112) (gh-…

1bcc0d1

…160183)

corona10 added a commit that referenced this pull request

Oct 22, 2026


          [3.15] gh-159111: Update vendored mimalloc to v2.5.2 (gh-159112) (gh-…

86e3b9f

…160178)

Reviewers

DinoV

DinoV approved these changes

ericsnowcurrently

Awaiting requested review from ericsnowcurrently

ericsnowcurrently is a code owner

ZeroIntensity

Awaiting requested review from ZeroIntensity

ZeroIntensity is a code owner

FFY00

Awaiting requested review from FFY00

FFY00 is a code owner

AA-Turner

Awaiting requested review from AA-Turner

AA-Turner is a code owner

erlend-aasland

Awaiting requested review from erlend-aasland

erlend-aasland is a code owner

emmatyping

Awaiting requested review from emmatyping

emmatyping is a code owner

itamaro

Awaiting requested review from itamaro

itamaro is a code owner

mpage

Awaiting requested review from mpage

methane

Awaiting requested review from methane

Uh oh!

There was an error while loading. Please reload this page.

Assignees

corona10

Labels

sprint type-feature

A feature request or enhancement

Projects

None yet

Milestone

No milestone

Development

Successfully merging this pull request may close these issues.

Uh oh!

There was an error while loading. Please reload this page.

5 participants

Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.

You are visitor 01402503 — GeezerVison does not store the pages you look up.
Best viewed with Netscape Navigator 4.7 or Internet Explorer 6 at 800×600. No cookies required.

GeezerVison

Conversation

corona10 commented Oct 10, 2026 • edited by bedevere-app Bot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

bedevere-bot commented Oct 10, 2026

Uh oh!

bedevere-bot commented Oct 10, 2026

Uh oh!

corona10 commented Oct 10, 2026

Uh oh!

read-the-docs-community Bot commented Oct 10, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Documentation build overview

Uh oh!

bedevere-bot commented Oct 10, 2026

Uh oh!

corona10 commented Oct 10, 2026

Uh oh!

bedevere-bot commented Oct 13, 2026

Uh oh!

mpage commented Oct 13, 2026

Uh oh!

mpage commented Oct 13, 2026

Uh oh!

corona10 commented Oct 13, 2026

Uh oh!

corona10 Oct 22, 2026

Choose a reason for hiding this comment

Uh oh!

corona10 Oct 22, 2026

Choose a reason for hiding this comment

Uh oh!

corona10 commented Oct 22, 2026

Uh oh!

DinoV left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

miss-islington-app Bot commented Oct 22, 2026

Uh oh!

miss-islington-app Bot commented Oct 22, 2026

Uh oh!

miss-islington-app Bot commented Oct 22, 2026

Uh oh!

bedevere-app Bot commented Oct 22, 2026

Uh oh!

bedevere-app Bot commented Oct 22, 2026

Uh oh!

Reviewers

Uh oh!

Assignees

Labels

Projects

Milestone

Development

Uh oh!

5 participants

corona10 commented Oct 10, 2026 •

edited by bedevere-app Bot

Loading

Uh oh!

There was an error while loading. Please reload this page.

read-the-docs-community Bot commented Oct 10, 2026 •

edited

Loading

Uh oh!

There was an error while loading. Please reload this page.